A capillary whole blood method for measuring the INR

Area of Science:

• Clinical Chemistry
• Hematology
• Diagnostic Methods

Background:

• Accurate monitoring of the international normalized ratio (INR) is crucial for patients on anticoagulant therapy.
• Traditional methods often rely on venous blood samples, which can be invasive and inconvenient.
• Point-of-care testing using capillary blood offers a potential alternative for easier INR monitoring.

Purpose of the Study:

• To describe and validate a novel method for measuring INR using native whole blood from capillary samples.
• To evaluate the accuracy and reliability of this capillary blood method compared to the standard venous blood method.
• To assess the influence of haematocrit variations and reagent stability on the capillary INR measurements.

Main Methods:

• A modified method utilizing Innovin recombinant thromboplastin for INR measurement on capillary blood samples was developed.
• Reagent modification was performed to address non-optimal calcium levels in the sample/reagent mixture.
• Results from the capillary method were compared against a standard venous blood method, and haematocrit effects were analyzed.

Main Results:

• Ninety-five percent of capillary INR results were within 0.42 INR (higher) or 0.38 INR (lower) of venous blood results.
• The method demonstrated minimal impact from changes in haematocrit levels.
• Satisfactory results were obtained, with no reagent drift observed when properly stored, and validated by UKNEQAS samples.

Conclusions:

• The described method provides a convenient, simple, and accurate approach for INR measurement using native capillary whole blood and Innovin recombinant thromboplastin.
• This capillary blood method offers a viable alternative to venous sampling for routine INR monitoring.
• The method's reliability is supported by its accuracy, minimal haematocrit interference, and reagent stability.